Watch the Southern Jam - Solo online guitar lesson by Jeff Scheetz from Rock Solid
One of the main things southern rock solos have is a strong melody. Lots of great southern rock solos are ones you can hum or sing along with (think "Freebird"). A lot of this melodic posturing can be attributed to the major pentatonic scale. Just like a lot of country players use this to great advantage, so do the southern rebels.
Check out solos on any Skynrd, Molly Hatchet, or Duane Allman release and you will hear it.